This invention relates to a data transmission system using a device for correcting errors in the received data and an error correcting method.
A conventional data transmission system, such as a disk reproducing device, comprises a receiving device 1 for receiving data, a temporary storage device 2 for storing the received data temporarily, an error correcting device 4 for correcting errors in the data temporarily stored, and a transmitting device 3 for transmitting the error-corrected data, as shown in FIG. 1.
As an example of data, consider the data received in this order: [d.sub.0,0, d.sub.0,1, d.sub.0,2, . . . , d.sub.0,M-1, d.sub.1,0, d.sub.1,1, . . . , d.sub.N-1,M-2, d.sub.N-1,M-1 ] as shown in FIG. 2, and assume that error correction codes P (internal code) and Q (external code) consisting of product codes as shown in FIG. 2 are added the data. In this case, information on the sensing of errors in the data codes using one correction code P, or the internal code, can be used for what is called an erasure correction using the other correction code Q, or the external code.
In the conventional system, the data recorded on a disk or the like is received by the receiving device 1. The received data is stored in the temporary storage device 2. An error correcting process using the error correction codes P and Q consisting of the product codes is performed on the data stored in the temporary storage device 2.
Specifically, the data stored in the temporary storage device 2 is called back to the error correcting device 4. The error correcting device 4 then executes a correcting process using the internal code P first. Because in the first correcting process, there is no error position information, erasure correction cannot be performed. In that case, the correcting process is performed on the data using only the internal code P and the result is stored in the temporary storage device 2.
Then, the data is called back again from the temporary storage device 2 to the error correcting device 4, which then performs a correcting process using the external code Q. In this correcting process, it is possible to perform erasure correction on the basis of information on the position of the error sensed in the correcting process of the internal code P, in addition to the correcting process using only the external code Q.
That is, with the conventional error correcting device, erasure correction cannot be performed in the first correcting process. After the first correcting process using the internal code P, however, when the correcting process using the external code Q is performed on the basis of information on the first correction, this achieves a sufficient correcting capability, even if erasure correction is not carried out in the first correcting process.
To do this, it is necessary to repeat the correcting process using the internal code P and the correcting process using the external code Q. Therefore, to perform error corrections at high speed, the data transfer rate between the error correcting device 4 and the temporary storage device 2 has to be increased.
An attempt to increase the data transfer rate between the error correcting device 4 and the temporary storage device 2 gives rise to an increase in the device size and in the power consumption resulting from the faster operation.